Floor insulation to cover joists [Version ID #94]

Author details

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Detail summary

Floor insulation detail for shallow/thin joists, with rigid insulation beneath to cover joists and improve airtightness.

Technical description

Section detail. Floor insulation for suspended timber floor. Insulation between and covering joists.

Preparation: Inspect sub-floor and timbers for signs of damp and rot. Before starting work carry out a survey of any structual timbers, particularly those which enter external walls (e.g. floor joists). Record current condition of timbers and moisture content for future reference.

Remove any organic matter from sub-floor and floor void. Ensure all existing air-bricks are unobstructed with clear ventilation path

Parts list

  • Rigid woodfibre insulation fixed across joist.

    Woodfibre insulation. Thickness: to create total 200mm insulation thickness (including woodfibre between joists). Thermal conductivity: .004W/m2K. GWP 0.

    Unger \ www.unger-diffutherm.de \ UdiDiffutherm

  • Woodfibre Insulation Between Suspended Ground Floor Joists

    Flexible woodfibre insulation. \ Depth TBC on site based on depth of existing joist. \ Friction fit between joists to ensure air-tightness (batts cut approx 20mm wider than opening between joists.) \ Thermal conductivity: .004W/m2K. GWP 0.

    Unger \ www.unger-diffutherm.de \ UdiFLEX

  • Seal between floorboards- existing ground floor.

    Draught-proof and seal all timber floors to ensure no air-leaks

    Draughtex. \ www.draughtex.co.uk \ Reference: Draughtex Neoprene Strips

  • Single-sided air seal tape

    Tape for junctions critical to air-tightness. 60mm (typical). \ Accesssories: ORCON F sealant and TESCON PRIMER RP (for use on rough/old surfaces to assist adhesion)

    Pro Clima \ http://www.greenbuildingstore.co.uk/page--pro-clima-airtightness-tapes-options.html \ TESCON VANA/ TESCON PROFIL (2 release tapes)


  1. Admin - 2015-04-30 13:26:33

    Introduction/summary updated to include references to undercroft/cellar as per title.

  2. Admin - 2015-04-30 11:13:07

    Reformatting changes. DWG file uploaded.

  3. Admin - 2015-03-30 11:10:07

    Preview image and pdf detail file updated.

  4. Admin - 2015-03-30 10:53:22

    DP09a amended for use on "joints of Rigid insulation board". Plasterboard part removed.

  5. Admin - 2015-03-26 13:51:36

    Removed reference to Approved document H.

  6. Admin - 2015-03-26 13:26:49

    General re-formatting. Introduction revised. Technical description updated with approved docs and additional notes.Parts list updated with supplier links.

  7. Admin - 2015-03-17 10:29:21

    Introduction updated, Technical description expanded. Parts list revised with relevant codes.

  8. Admin - 2015-03-04 15:54:25 [Displayed version]

    First version

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